1. Field of the Invention
The invention is related to the field of magnetic recording head fabrication, and in particular, to improved methods of fabricating a magnetoresistance sensor that is pinned by an etch induced magnetic anisotropy.
2. Statement of the Problem
Magnetic disk drive systems typically include a magnetic disk, a sensor head having a write element and a magnetoresistance (MR) read sensor, a suspension arm, and an actuator arm. As the disk rotates air adjacent to the disk surface moves with the disk. This allows the sensor to fly on an extremely thin cushion of air, generally referred to as an air bearing. When the sensor flies on the air bearing, the actuator arm swings the suspension arm to place the sensor over selected circular tracks on the rotating magnetic disk where signal fields are written to and read by the write and read elements, respectively. The write and read elements are connected to processing circuitry that operates according to a computer program to implement write and read functions.
The most common type of sensors are magnetoresistance (MR) read elements. One type of MR read element is a Giant MR (GMR) read element. GMR read elements may have two layers of ferromagnetic material (e.g., CoFe) separated by a non-magnetic spacer layer (e.g., Cu). These type of GMR read elements are typically referred to as spin valve elements (SV). A simple-pinned SV read element generally includes an anti-ferromagnetic (AMF) pinning layer (e.g., PtMn) which pins a ferromagnetic pinned layer (e.g., CoFe). The ferromagnetic pinned layer has its magnetization fixed by exchange coupling with the AFM pinning layer. The AFM pinning layer generally fixes the magnetic moment of the ferromagnetic pinned layer perpendicular to the air bearing surface (ABS) of the recording head. SV elements further include a non-magnetic spacer layer (e.g., Cu) separating the pinned layer from a ferromagnetic free layer (e.g., CoFe). The magnetization of the ferromagnetic free layer is not fixed and is free to rotate in response to an external magnetic field from the magnetic disk.
Another type of SV read element is an anti-parallel (AP) pinned SV read element. The AP-pinned SV read element differs from the simple pinned SV read element in that an AP-pinned structure has multiple thin film layers forming the pinned layer structure instead of a single pinned layer. The pinned layer structure includes a first ferromagnetic pinned (keeper) layer (e.g., CoFe), a non-magnetic spacer layer (e.g., Ru), and a second ferromagnetic pinned (reference) layer (e.g., CoFe). The first ferromagnetic pinned (keeper) layer has a magnetization oriented in a first direction perpendicular to the ABS by exchange coupling with the AFM pinning layer. The second ferromagnetic pinned (reference) layer is anti-parallel coupled with the first ferromagnetic pinned (keeper) layer across the spacer layer. Accordingly, the magnetization of the second ferromagnetic pinned (reference) layer is oriented in a second direction that is anti-parallel to the direction of the magnetization of the first ferromagnetic pinned (keeper) layer.
Another type of MR read element is a Tunneling MR (TMR) read element. TMR read elements differ from GMR elements in that a thin, electrically insulating, tunnel barrier layer (e.g., aluminum oxide or magnesium oxide) is used between the ferromagnetic pinned layer and the ferromagnetic free layer instead of a non-magnetic spacer layer (e.g., Cu). The TMR read elements may be simple pinned or AP-pinned as with the GMR read elements.
There are several problems with using AFM pinning layers in read sensors. First, including an AFM pinning layer consumes a large fraction of the limited space available in the read gap of the SV read element. As the recording density in magnetic storage devices becomes larger, it is becoming more important to fabricate smaller SV elements. Second, in current perpendicular to plane (CPP) sensors, the current flows through the AFM pinning layer. Because conventional AFM materials have high resistivity, the sensing signal of the SV element is effectively reduced by the parasitic resistance of the AFM layer. It is evident from the above discussion that improved solutions are needed for pinning the magnetic pinned layer in magnetoresistance sensors for high density magnetic recording heads.